Hi,
Today I have worked with an old diesel car. Since the car have some issue I made some measurement with my dmm. I post one picture to bette explain my case. When I put the probe on wire A and B I got:
2.5vcc
450hz
duty cycle 2%

When I put the probe between chassis ground and A wire I got:
12.5vcc
Frequency =0Hz


When I put the probe between chassis ground and B wire I got:
10 vcc.
Frequency =0Hz

This solenoid is a shut off valve he have non sense to control it with pwm. I sure he always need only on or off.

Is there any sense of my measurement?

 

It makes perfect sense.

A is 12.5V above the 0V chassis reference.
B is 10.0V above the 0V chassis reference.
A-B is the difference, 2.5V.
Using a PWM signal to manage valves on engines is common. You any be mistaken about the open-closed nature of the valve—it may be feathered by the ECM at points in the engine’s starting, stopping, or running cycles.

 

Hi,
Today I have worked with an old diesel car. Since the car have some issue I made some measurement with my dmm. I post one picture to bette explain my case. When I put the probe on wire A and B I got:
2.5vcc
450hz
duty cycle 2%

When I put the probe between chassis ground and A wire I got:
12.5vcc
Frequency =0Hz


When I put the probe between chassis ground and B wire I got:View attachment 310132
10 vcc.
Frequency =0Hz

This solenoid is a shut off valve he have non sense to control it with pwm. I sure he always need only on or off.

Is there any sense of my measurement?

What does the solenoid do? Is it the fuel shut-off valve?
Is it a non-common-rail diesel, where the speed control is a mechanical link to the injector pump? ("old" is a relative term, and we have had common-rail diesels for over 20 years now)
If it is the fuel shut-off valve, then I would not expect any other position than "open" or "closed"

 

Hi and thank you both for your replies

Using a PWM signal to manage valves on engines is common.

Why I can't see the pwm when I put one probe on chassis and the other on the wire A or B?

Is it the fuel shut-off valve?

Yes, this is a shut-off valve.
On this pump the shut-off valve have only tow state or off.

 

I think that the readings are spurious.
Is one side of the valve permanently connected to the battery positive? And the other side grounded by the "engine stop" switch?
What do you get if you repeat the readings with a 1k resistors across the meter probes?

 

It's a Fluke dmm but I will do you test with the resistor.

 

It's a Fluke dmm but I will do you test with the resistor.

Fluke meters have 10MΩ impedance. If the wiring is disconnected (e.g. not switched on) then it will measure any voltage that the wiring picks up.